In magnetic media storage systems for computers, such as hard disk drives, digital data is used to modulate the current in a read/write head coil so that a sequence of corresponding magnetic flux transitions are written onto a magnetic medium in data tracks. To read this recorded data, the read/write head passes over the magnetic medium and transduces the magnetic transitions into pulses of an analog signal that alternates in polarity. The analog signal is provided to and decoded by read channel circuitry to reproduce the digital data.
A block diagram of a storage media system and a read channel is illustrated in FIG. 1. The storage media system 10 includes a storage medium 12, a read/write head 14 and a pre-amplifier 16. The read/write head 14 writes information to and reads information from the magnetic medium 12. While only a single storage medium 12 and read/write head 14 are shown in the block diagram of FIG. 1, it should be apparent to those skilled in the art that the storage media system may include multiple storage media and read/write heads from which data can be written to or read from. Within the storage media system 10, the read/write head 14 is coupled to the pre-amplifier circuit 16 to provide an analog output signal An Out representing the data read from the magnetic medium 12.
The read channel 22 is typically included on the motherboard 20 within the host system. Among other circuits, the read channel 22 includes an amplifier 24, a filter 26 and a peak detection circuit 28. The analog output signal An Out from the pre-amplifier circuit 16 is coupled as an input to the amplifier 24. An output of the amplifier 24 is coupled to the filter 26. An output of the filter 26 is coupled to the peak detection circuit 28. A clock signal 30 from the motherboard is also coupled to the peak detection circuit 28. A read channel output signal RD from the peak detection circuit 28 is coupled to a host system bus 32 in order to provide the digital representation of the analog signal output from the storage media system 10 to other components within the host system. This digital representation represents the data read from the storage medium 12.
Within a hard disk drive, to optimize the performance of the hard disk drive, the necessary read output impedance will depend on the system in which the hard disk drive is included and the configuration of the components within the system. For example, the distance from the hard disk drive to the read channel will be a factor in determining the optimum read output impedance. It is likely that the optimal read output impedance will be different for different systems and different system configurations. For a designer of a hard disk drive, it is therefore necessary to include multiple read output impedances in order to provide alternatives to optimize the performance for the hard disk drive with each specific system and system configuration.
A conventional read amplifier output circuit is illustrated in FIG. 2. The read amplifier output circuit 40 includes the read amplifier 42, the several resistors 44, 46 and 48, each having a different impedance and the output 50. In order to adjust the output impedance of the read output, metal line traces are routed from the output read amplifier 42 to the appropriate resistor 44, 46 or 48 for the application and then from the appropriate resistor to the output 50. In this manner, the read output impedance can be adjusted by utilizing the appropriate resistor within the read output circuit. By having multiple resistors available on the integrated circuit chip, the read output impedance can be optimized for a particular application or system by routing the traces to include the appropriate resistor in the read output circuit. In the example illustrated in FIG. 2, the traces are routed to include the resistor 46 in the read output circuit.
This method of adjusting the resistance is not ideal because it requires that multiple resistors are included on the integrated circuit chip including the read amplifier output circuit.